In the related art, a high-conductivity and high-strength copper alloy sheet is used as components, such as a connector, a terminal, a relay, a spring, and a switch, which are used in electrical components, electronic components, automobile components, communication apparatuses, and electronic and electrical apparatuses. However, along with a reduction in the size and weight of such apparatuses of recent years and an improvement in performance, components which are used for the apparatuses have also been required to have extremely strict characteristic improvement and cost performance. For example, an ultra-thin sheet is used in a spring contact portion of a connector. In a high-strength copper alloy constituting such an ultra-thin sheet, in order to reduce the thickness thereof, a high strength and a high balance between elongation and strength are required. Further, high productivity, particularly, superior economic efficiency is required by suppressing use of copper, which is a noble metal, to a minimum.
As a high-strength copper alloy, phosphor bronze for a spring and nickel silver for a spring are known. As a high-conductive and high-strength copper alloy which is commonly used and superior in cost performance, brass is well-known in the related art. These well-known high-strength copper alloys have the following problems and cannot satisfy the above-described requirements.
Phosphor bronze and nickel silver are poor in hot workability and are difficult to manufacture by hot-rolling, and thus are typically manufactured by horizontal continuous casting. Accordingly, productivity is poor, energy cost is high, and the yield is poor. In addition, phosphor bronze and nickel silver, which are representative high-strength alloys, contains a large amount of copper which is a noble metal or contains a large amount of Sn or Ni which is expensive. Therefore, there is a problem in economic efficiency, and conductivity is poor. In addition, since these alloys have a high density of approximately 8.8, there is a problem of a reduction in the weight of the apparatuses.
Brass is inexpensive but it is not satisfactory in terms of strength. Therefore, brass is inappropriate as the above-described small-sized and high-performance product component.
Accordingly, such high-conductive and high-strength copper alloys cannot satisfy requirements as components of various kinds of apparatuses which require superior cost performance, a reduction in size and weight, and an improvement in performance. Therefore, the development of a new high-strength copper alloy has been strongly demanded.
As an alloy for satisfying the above-described requirements of high conductivity and high strength, for example, a Cu—Zn—Sn alloy disclosed in Patent Document 1 is known. However, the alloy disclosed in Patent Document 1 does not have a sufficient strength as well.
Among common components such as a connector, a terminal, a relay, a spring, and a switch which are used in electrical components, electronic components, automobile components, communication apparatuses, and electronic and electrical apparatuses, there are components and portions which require a higher strength for reducing the thickness on the condition that elongation and bending workability are superior, and there are components and portions which require higher conductivity and stress relaxation characteristics for causing a high current to flow. However, strength and conductivity are properties contradictory to each other. In general, if a strength is improved, conductivity is decreased. Under these circumstances, a high-strength component is known which requires a tensile strength of, for example, 540 N/mm2 or higher and a conductivity of 21% IACS or higher, for example, approximately 25% IACS. Specifically, this component is used as a connector or the like and has a high strength and superior cost performance on the condition that elongation and bending workability are sufficient. Incidentally, regarding cost performance, not only copper belonging to noble metals but also elements having a cost higher than or equal to that of copper are not used in large amounts. Specifically, the total content of copper and elements having a cost higher than or equal to that of copper is suppressed to be at least less than or equal to 71.5 mass % or less than or equal to 71%. In addition, the density of the alloy is decreased to be less than 8.94 g/cm3, which is the density of pure copper, and less than 8.8 g/cm3 to 8.9 g/cm3, which is the density of the above-described phosphor bronze and the like, by approximately 3%. Specifically, the density of the alloy is set to be at least less than or equal to 8.55 g/cm3. As the density is decreased, a specific strength is increased correspondingly, which leads to cost reduction. In addition, the weight of a component can also be decreased.